Abstract
The exceptional diversity of life among regions and taxonomic clades on Earth has fascinated
people since the days of Humboldt, Wallace and Darwin. Through meticulous study,
scientists attempt to elucidate the factors responsible for generating this diversity. It is widely
held, however, that the variation in species diversity among evolutionary clades and
geographic regions must ultimately reflect variation in the processes of speciation and
extinction. Moreover, variation in diversity among geographic regions may also reflect
differences in the movement of lineages between regions, just as variation in morphological
diversity is influenced by variation in the rates at which phenotypic traits evolve. However,
our understanding of the relative importance of these processes, and the factors that influence
them remain inadequate.
In this thesis, I have attempted to contribute to the growing body of work that has assessed
these issues. To do so, I have used the large radiation of passerine birds as a model system –
for several reasons. First, following decades of research, our understanding of the
phylogenetic relationships and systematics of passerine birds is extensive, aided by the rapid
development of DNA sequencing techniques and methods of phylogenetic inference. Second,
given the relative ease at which birds can be studied in the field, knowledge of the geographic
distributions, life history and ecology of passerine birds is significantly better than for most
other organismal groups. Most importantly however, passerine birds exhibit dramatic
variation in diversity among regions and clades. Together, these factors ensure that Passerine
birds represent an ideal group for assessing macroecological and macroevolutionary
questions, and unsurprisingly, they have served as a model system for the assessment of a
wide range of such trends in recent decades.
Despite this, our understanding of the factors that have shaped passerine diversity gradients is
still incomplete. Thus, questions such as whether particular traits have facilitated passerine
diversification remain largely unanswered. In this thesis, I have taken advantage of recent
improvements in our estimates of passerine phylogenetic relationships, trait diversity and
novel comparative methods to address such questions. In addition, a core component of the
thesis has been devoted to the generation of additional, new data, including both new DNA
sequences and species trait data. Although I have focused on passerine birds throughout, both
the taxonomic and spatial scale, and the specific aims of each study has varied considerably.
In the first chapter, I tested the hypothesis that variation in the modes of parental care has
had an influence on rates of diversification and geographic expansion in the globally
distributed Corvides radiation (ca. 800 species). In the second and third chapters, I
generated new phylogenetic and morphological trait data for the Australasian Meliphagides
radiation (ca. 300 species), to assess whether an ancestral shift in diet influenced the
evolution of extensive morphological diversity and species accumulation in the adaptive
radiation of honeyeaters. In the fourth chapter, I explored phylogenetic relationships and
species limits in a small radiation of Australasian shrikethrushes (genus Colluricincla, 5
currently recognized species). In the fifth and final chapter, I have explored the
morphological diversity of spermatozoa across all passerines (ca. 6,000 species), with a
particular focus on whether the rates at which sperm evolves exhibits a signature of amonglineage
variation.
Together, my analyses have provided robust support for many of the above hypotheses. I
present evidence of widespread variation in the rates at which both species and
morphological diversity evolves and accumulates and in the extent of geographic expansion
among clades. Importantly, I find that much of this variation can be linked to key differences
in life history strategies and ecology among different species and groups. An important
implication of these findings however, is that the causes of variation in geographic
distributions, and species and morphological diversity among passerine birds, are multifaceted
and have likely been shaped by a variety of different processes. Continued research
into how these factors interact, and the genetic architecture underlying them, offers great
potential in terms of elucidating the relative contribution of the processes that determine
biodiversity gradients.
people since the days of Humboldt, Wallace and Darwin. Through meticulous study,
scientists attempt to elucidate the factors responsible for generating this diversity. It is widely
held, however, that the variation in species diversity among evolutionary clades and
geographic regions must ultimately reflect variation in the processes of speciation and
extinction. Moreover, variation in diversity among geographic regions may also reflect
differences in the movement of lineages between regions, just as variation in morphological
diversity is influenced by variation in the rates at which phenotypic traits evolve. However,
our understanding of the relative importance of these processes, and the factors that influence
them remain inadequate.
In this thesis, I have attempted to contribute to the growing body of work that has assessed
these issues. To do so, I have used the large radiation of passerine birds as a model system –
for several reasons. First, following decades of research, our understanding of the
phylogenetic relationships and systematics of passerine birds is extensive, aided by the rapid
development of DNA sequencing techniques and methods of phylogenetic inference. Second,
given the relative ease at which birds can be studied in the field, knowledge of the geographic
distributions, life history and ecology of passerine birds is significantly better than for most
other organismal groups. Most importantly however, passerine birds exhibit dramatic
variation in diversity among regions and clades. Together, these factors ensure that Passerine
birds represent an ideal group for assessing macroecological and macroevolutionary
questions, and unsurprisingly, they have served as a model system for the assessment of a
wide range of such trends in recent decades.
Despite this, our understanding of the factors that have shaped passerine diversity gradients is
still incomplete. Thus, questions such as whether particular traits have facilitated passerine
diversification remain largely unanswered. In this thesis, I have taken advantage of recent
improvements in our estimates of passerine phylogenetic relationships, trait diversity and
novel comparative methods to address such questions. In addition, a core component of the
thesis has been devoted to the generation of additional, new data, including both new DNA
sequences and species trait data. Although I have focused on passerine birds throughout, both
the taxonomic and spatial scale, and the specific aims of each study has varied considerably.
In the first chapter, I tested the hypothesis that variation in the modes of parental care has
had an influence on rates of diversification and geographic expansion in the globally
distributed Corvides radiation (ca. 800 species). In the second and third chapters, I
generated new phylogenetic and morphological trait data for the Australasian Meliphagides
radiation (ca. 300 species), to assess whether an ancestral shift in diet influenced the
evolution of extensive morphological diversity and species accumulation in the adaptive
radiation of honeyeaters. In the fourth chapter, I explored phylogenetic relationships and
species limits in a small radiation of Australasian shrikethrushes (genus Colluricincla, 5
currently recognized species). In the fifth and final chapter, I have explored the
morphological diversity of spermatozoa across all passerines (ca. 6,000 species), with a
particular focus on whether the rates at which sperm evolves exhibits a signature of amonglineage
variation.
Together, my analyses have provided robust support for many of the above hypotheses. I
present evidence of widespread variation in the rates at which both species and
morphological diversity evolves and accumulates and in the extent of geographic expansion
among clades. Importantly, I find that much of this variation can be linked to key differences
in life history strategies and ecology among different species and groups. An important
implication of these findings however, is that the causes of variation in geographic
distributions, and species and morphological diversity among passerine birds, are multifaceted
and have likely been shaped by a variety of different processes. Continued research
into how these factors interact, and the genetic architecture underlying them, offers great
potential in terms of elucidating the relative contribution of the processes that determine
biodiversity gradients.
| Originalsprog | Engelsk |
|---|
| Forlag | Natural History Museum of Denmark, Faculty of Science, University of Copenhagen |
|---|---|
| Status | Udgivet - 2017 |